Although various synthesized compounds having inhibitory actions against harmful pests have hitherto been used as insecticides, almost all of them belong to organic phosphate esters, carbamic esters, organic chlorine-containing compounds or pyrethroid compounds.
On the other hand, it has been reported that 1-arylpyrazole derivatives, wherein the 3-position of a pyrazole ring is a hydrogen atom, an alkyl group, a cycloalkyl group, a halogenoalkyl group, a cyano group, a nitro group, a halogen atom, a carbamoyl group or a thiocarbamoyl group have an insecticidal activity (U.S. Pat. No. 5,232,940 corresponding to JP-A 228065/1987, U.S. Pat. No. 4,771,066 corresponding to JP-A 207259/1987, U.S. Pat. No. 5,236,938 corresponding to JP-A 148240/1993, EP-A 385809, U.S. Pat. No. 5,306,694 and WO93/06089).
These pyrazole derivatives have insecticidal actions, however, they have high toxicities to human beings, domestic animals and fish. Sometimes, the pyrazole derivatives exhibit toxicity to natural enemies of pests, and a high residual property in soil or the like. Therefore, a satisfactory effect is not actually obtained at present.
In order to solve the above problems, the present inventors have intensively studied for a long time so as to find out an insecticide having a structure which is quite different from that of an insecticide which has hitherto been used. As a result, it has been unexpectedly found that a novel pyrazole derivative or a salt thereof has a very strong insecticidal activity. It has also been found that the pyrazole derivative or a salt thereof is safe because it causes little chemical damage to plants and it's toxicity to human being, domestic animals, fish, natural enemies of pests, etc. is low. Furthermore, the present inventors have intensively studied based on these findings and completed the present invention.